It is known in the art to use spacer structures between the cathode and anode of a field emission display. The spacer structures maintain the separation between the cathode and the anode. They must also withstand the potential difference between the cathode and the anode.
However, spacers can adversely affect the flow of electrons toward the anode in the vicinity of the spacer. Some of the electrons emitted from the cathode can cause electrostatic charging of the surface of the spacer, changing the voltage distribution near the spacer from the desired voltage distribution. The change in voltage distribution near the spacer can result in distortion of the electron flow.
In a field emission display, this distortion of the electron flow proximate to spacers can result in distortions in the image produced by the display. In particular, the distortions can render the spacers "visible" by producing a dark region in the image at the location of each spacer or the distortions can produce a "bright spot" near the spacer.
Several prior art spacer structures attempt to solve the problems associated with spacer related electron flow distortion. These include spacers coated with a charge bleed layer, spacers made of high-capacitance materials and the placing of independently controlled electrodes along the height of the spacer for controlling the voltage distribution near the spacer. Coated spacers and spacers with independently controlled electrodes are susceptible to mechanical damage and/or alteration, such as may occur during the handling of the spacers. Coated spacers are also susceptible to chemical alteration, which may change their resistivity. These prior art methods also add additional processing steps and cost to field emission display fabrication. In addition, the prior art methods do not adequately eliminate the spacer visibility problem over the whole luminance range of the field emission display.
Accordingly, there exists a need for a method of controlling spacer visibility over the entire luminance range of the field emission display that eliminates the need for expensive and complex prior art methods of controlling spacer related electron flow distortion.